Origin: Greek prefix mono-
Monotone has 7 different meanings across 2 categories:
a single tone repeated with different words or different rhythms (especially in rendering liturgical texts)
"The priest's delivery of the ancient psalms was so monotone that his voice seemed to hum a single, unchanging note despite the shifting cadence of the prayers."
A single unvaried tone of speech or a sound.
"Her voice remained in a flat, monotone drone throughout the entire lecture, making it hard to stay awake."
To speak in a monotone.
"The delivery man spoke in such a flat, unvarying voice that I couldn't tell if he was annoyed or just reading his list."
sounded or spoken in a tone unvarying in pitch
"the owl's faint monotonous hooting"
Having a single unvaried pitch.
"The news anchor delivered the breaking update in such a monotone voice that it sounded like a robot reading a manual."